The IDirectSound3DListener::SetDistanceFactor method sets the current distance factor.
HRESULT SetDistanceFactor(
  D3DVALUE flDistanceFactor,  
  DWORD dwApply               
);
 If the method succeeds, the return value is DS_OK.
If the method fails, the return value may be DSERR_INVALIDPARAM.
For additional information about distance factors, see Distance Factor.
  Windows NT/2000: Requires Windows 2000.
  Windows 95/98: Requires Windows 95 or later. Available as a redistributable for Windows 95.
  Header: Declared in dsound.h.
  Import Library: Use dsound.lib.